The formulation of lubricants typically includes an additive package incorporating a variety of chemicals to improve or protect lubricant properties in application specific situations, particularly internal combustion engine and machinery applications. The more commonly used additives include oxidation inhibitors, rust inhibitors, antiwear agents, pour point depressants, detergent-dispersants, viscosity index (VI) improvers, foam inhibitors and the like. This aspect of the lubricant arts is specifically described in Kirk-Othmer "Encyclopedia of Chemical Technology", 3rd edition, Vol. 14, pp477-526, incorporated herein by reference. Considering the diversity of chemical structures represented by the plethora of additives incorporated in a typical lubricant formulation, and the quantity in which they are added, the artisan in the lubricant formulation arts faces a substantial challenge to provide a homogeneous formulation which will remain stable or in solution during inventory and during use. Lubricants, particularly synthetic lubricants of the type of interest in the instant invention, are usually hydrogenated olefins. Due to their hydrocarbon structure they are largely incompatible with polar additives such as antioxidants, antirust and antiwear agents, etc. Accordingly, in order to render the lubricants compatible with the polar additives large amounts of expensive polar organic esters must be added to the formulation. Useful commercial formulations may contain 20% percent or more of such esters as bis-tridecanol adipate for example, solely to provide a fully homogeneous lubricant blend of lubricant and additive.
Modifying the solvent properties of lubricants with solubilizing agents such as organic esters, while solving the problem of how to prepare stable blends with lubricant additives, creates or accentuates other performance related problems beyond the added burden on cost of the product. The vulnerability of solubilizing agents to oxidative degradation promoting the formation of tars and gums must be taken into account. Seal swelling properties may be changed. Seal swell measures the ability of a lubricant to swell a seal, thus enhancing its sealing function. Solubilizing agents may effect viscometric properties such as viscosity and viscosity index of the material. When materials deficient in these properties are added in large amounts, the lubricant's effectiveness will be impaired. In view of these complications it is evident that novel approaches are called for in the modification or formulation of lubricants to incorporate additives without compromising properties or adding significantly to the cost of the product.
One approach to improve lubricant compatibility with additives is to add polar groups to the structure of the lubricant. Lubricants, in particular synthetic lubricants, are known to contain olefinic unsaturation and it has been determined in the present invention that such unsaturation can be effectively utilized to react with polar groups to add a polar functionality on to the lubricant molecule. The added polar group in the lubricant has sufficient solubilizing character to adequately dissolve additive packages without the addition of solubilizing agents such as adipate esters. It has been discovered in the instant invention that the necessary functionality i.e., functional group, can be added to the lubricant by reacting the lubricant olefinic group with an electronegative enophile. Depending upon the structure of the molecule added to the olefin unsaturation of the lubricant other property improvements typical of additive packages may also be conferred upon the lubricant mixture.
Recently, novel lubricant compositions (referred to herein as HVI-PAO and the HVI-PAO process) comprising polyalpha-olefins and methods for their preparation employing as catalyst reduced chromium on a silica support have been disclosed in U.S. patent applications Ser. Nos. 210,434 and 210,435, now U.S. Pat. Nos. 4,827,073 and 4,827,064 filed Jun. 23, 1988, incorporated herein by reference in their entirety. The process comprises contacting C.sub.6 -C.sub.20 1-alkene feedstock with reduced valence state chromium oxide catalyst on porous silica support under oligomerizing conditions in an oligomerization zone whereby high viscosity, high viscosity index (VI) liquid hydrocarbon lubricant is produced having branch ratios, i.e. CH.sub.3 /CH.sub.2, less than 0.19 and pour point below -15.degree. C. The process is distinctive in that little isomerization of the olefinic bond occurs compared to known oligomerization methods to produce polyalpha-olefins using Lewis acid catalyst. Lubricants produced by the process cover the full range of lubricant viscosities and exhibit a remarkably high viscosity index (VI) and low pour point even at high viscosity. The assynthesized HVI-PAO oligomer has a preponderance of terminal olefinic unsaturation or exo-olefinic groups, e.g., vinylidene groups.
It is an object of the present invention to provide novel derivatives of HVI-PAO oligomers containing polar functional groups suitable as lubricant additives.
Another object of the present invention is to provide methods for the production of HVI-PAO lubricants containing polar functional groups that provide superior additive properties.
Yet another object of the present invention is to incorporate polar groups in HVI-PAO lubricants by addition of electronegative groups to lubricant olefinic unsaturation.